THE UNION OF OXYGEN WITH HEMOGLOBIN 123 



He then determined the value of K by averaging a great number 

 of impossibly divergent determinations and calculated the curve. 

 The one respect in which he tried to verify his theory was that of 

 ascertaining whether the haemoglobin was present in the form of single 

 molecules. For this purpose he, in collaboration with Gansser, deter- 

 mined the osmotic pressure and found that it corresponded to a 

 molecular weight of 16,670, and therefore involves but a single atom 

 of iron in the molecule. The osmotic pressure of haemoglobin is the 

 subject of another chapter; how Hiifner and Gansser managed to 

 obtain the figure for it, which agreed so well with their theory, must 

 remain for ever a mystery. 



Bohr's theory (6). Bohr approached the matter from a standpoint 

 precisely opposite to that of Hiifner. He determined a dissociation 

 curve with great accuracy, and then tried to fit an equation based 

 upon some theoretical reasoning to the curve. The theory which 

 yielded, to him, a satisfactory solution was as follows : haemoglobin 

 consists of two substances united together, the protein and the 

 iron-containing part, which he called "haemochrome." When oxy- 

 haemoglobin was formed the oxygen broke up the combination 

 dissociating the haemochrome from the globin. Thus a double de- 

 composition took place. 



There is no further evidence for Bohr's theory than that which he 

 adduced, namely, that with its aid you can draw a curve which 

 coincides very closely with the one he determined. No attempt has, 

 as far as I know, been made to stretch the theory so as to include 

 the great number of curves which have since been brought to light 

 under different circumstances. Possibly such an attempt could be 

 made with success if one assumed that the affinity of the "haemo- 

 chrome for the oxygen" varied with the conditions, being very grea^ 

 in circumstances under which the curve approached most nearly 

 to a hyperbola, so that under such conditions there was little or no 

 dissociation of the pigment from the globin. 



HiU's theory (7), (8). It is natural that all theories should reflect the 

 times in which they are deduced. Whether or not they stand the test 

 of time depends in a measure on whether the knowledge in existence 

 at the time they are produced is sufficient to represent the whole truth. 



At the time when Hill produced his theory, and when Douglas, 

 Haldane and Haldane(9) pubhshed their expansion of it, the authors 

 in question had at their disposal a knowledge of colloid chemistry 

 which was denied to Hiifner and to Bohr. 



